JPH0335869A - Reflow furnace - Google Patents

Abstract

PURPOSE:To prevent detachment and dropping of firstly soldered parts from a substrate with the remelt of a solder by using a reflow furnace providing a preheating part having face heaters at upper and lower parts and a soldering part having the face heater only at one side at the time of soldering the parts on both faces of the substrate. CONSTITUTION:The substrate 7, on which the parts are to be soldered, is placed on an endless belt conveyor 6 and passes through the reflow furnace 1, and the parts are soldered on both faces of substrate 7. At the upper and lower parts of the belt conveyor 6 in the furnace, temp. raising part B1 composed of the face heaters 2a, 2b for heating the substrate 7, the substrate preheating part B providing soaking part B2 composed of two pairs of the face heaters 3a, 3b and 4a, 4b and successively, the main heating part A for soldering having the face heater 5a only at the upper face, are disposed. At the time of soldering the parts on the reverse face in the main heating part A by turning over the substrate 7 where the parts are already soldered on the one side face, as the face heater is not provided on the face side where the parts are already soldered, the detachment and dropping of the parts once soldered caused by remelt of the solder are prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a reflow oven used when surface-mounting parts such as semiconductor elements on a circuit board by soldering, and more specifically relates to a reflow oven used when surface-mounting components such as semiconductor elements on a circuit board. The present invention relates to a reflow oven suitable for use in mounting.

(Prior Art) Components such as various semiconductor elements are surface-mounted on printed circuit boards incorporated into electronic devices and the like.

In this case, surface mounting generally involves placing a component whose bonded portion is coated with solder at a predetermined position on the board surface, and then passing it through a reflow oven (described later) and heating it to a predetermined temperature to re-apply the solder. This is done by melting and soldering the components to the board.

Regarding the conventional structure reflow oven used for this surface mounting,
This will be explained with reference to FIG. FIG. 4 is a configuration diagram showing the conventional reflow oven side. First, in the figure, inside the furnace body l, there are a pair of surface heaters 2a-2b facing each other with a predetermined interval above and below.

Plural pairs of surface heaters such as 3a-3b, 4a-4b, and 5a-5b are arranged in series in the furnace length direction. Infrared heaters and far-infrared heaters are generally used as surface heaters.

A reherto conveyor 6 is disposed between each surface heater and runs from the entrance 1a to the exit 1b of the furnace body by a drive roller 9 connected to a motor 8 and three feed rollers 1o.

Boards 7 on which parts to be soldered are mounted are placed on the belt conveyor 6 at predetermined intervals in the furnace length direction, so that the boards 7 are transported from the inlet 1a to the outlet 1b. It will be done.

The substrate 7 carried into the furnace body 1 is first placed on the surface heaters 2a-2b.
It is rapidly heated to rise to a temperature, then uniformly heated by the surface heaters 3a-3b and 4a-4b, and soldering is performed by radiation heating from the surface heaters 5a-5b. Therefore, in this reflow oven, the region of the surface heaters 5a-5b constitutes the main heating section A,
The region located before this constitutes a preheating section B for optimizing soldering conditions in the main heating section A. In this preheating section B, surface heaters 2a-2b
The part is the temperature rise part Bl+ surface heater 3a3b, 4a
The part -4b is the soaking part B2. Here, the manner in which the substrate 7 is heated in each heating section is a combination of radiant heating received from the upper and lower surface heaters and heating by natural convection in the furnace atmosphere.

The board 7 to which the mounted components are soldered in the main heating section A is
It is carried out of the furnace through the outlet 1b of the furnace body, and at the time it is carried out from the furnace, by blowing air from the cooling fan 11 or air at a temperature lower than the furnace atmosphere temperature onto the soldered surface. Joints of mounted components are forcedly cooled.

(Problems to be Solved by the Invention) Recently, due to the increasing demand for high-density packaging, various components have been mounted on both sides of a printed circuit board.

When this double-sided mounting is carried out using a reflow oven with the conventional structure described above, first, a predetermined component is mounted on one side of the board and soldered by passing it through the reflow oven, and then the obtained board is soldered. A method is adopted in which the device is turned over, other predetermined components are mounted on the other side, and the mounted components are soldered by passing it through the reflow oven again.

During this second soldering operation, in the main heating section A,
This means that the parts that have already been soldered are being reheated by the lower surface heater 5b.

Therefore, during the process of passing through the main heating section A, the solder remelts at the joints of mounted components that have already been soldered, and the mounted components are likely to fall when removed from the furnace. To avoid such problems,
You can use high-temperature solder for the first soldering on one side, and low-temperature solder for the second soldering on the other side. It becomes necessary.

The present invention aims to solve the above-mentioned problems and provide a reflow oven that can perform double-sided mounting even when using one type of solder.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a preheating section and a main heating section are provided in which a plurality of pairs of surface heaters vertically facing each other are arranged in the furnace length direction. In a reflow furnace in which a workpiece is conveyed between a pair of side heaters, the lower side heater of the main heating section is removed, or the vicinity of the terminal end of the main heating section is removed. Provided is a reflow oven characterized in that a cooling means is provided at a lower part of the oven for introducing outside air or air at a temperature lower than the temperature of the atmosphere inside the oven.

(Function) In the main heating section when passing through the reflow oven for the second time, the temperature of the upper surface of the substrate does not decrease due to radiation heating from the surface heater.
On the other hand, the bottom surface of the board, that is, the surface to which mounted components have already been soldered, is not heated by the surface heater or is cooled by the atmosphere, which is lower than the atmosphere in the furnace, so that solder does not form at the joints of mounted components. Re-melting does not occur, and as a result, it is possible to prevent mounted components from falling due to this. At that time, the temperature of the top surface of the board is maintained at a temperature suitable for soldering, so other mounted components can be soldered there.

(Example) Embodiments of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of a reflow oven of the present invention, in which the same elements as in FIG. 4 are designated by the same reference numerals.

The reflow furnace shown in Figure 1 is the main heating section A of the furnace shown in Figure 3.
It has a structure in which the surface heater 5b located below is removed. In this structure, the upper surface of the substrate 7 is radiantly heated by the upper surface heater 5a during the process of passing through the main heating section A, but the lower surface is not heated by the surface heater.

Therefore, even in the process of soldering on the upper surface of the board 7, the solder at the joints of the mounted components that have already been soldered on the lower surface of the board 7 will not re-melt, and when the solder is carried out from the outlet ib of the furnace, the mounted components will not melt again. No more falling parts.

FIG. 2 is a block diagram of another embodiment of the present invention.

In the case of this furnace, the lower surface heater 5 in the main heating section A
b' is made shorter in the furnace length direction than the surface heater 5b in FIG.
This main heating section A has a structure in which a cooling means 12 is disposed below near the terminal end thereof.

The cooling means 12 consists of a pipe 12a of a predetermined diameter that opens near the bottom surface of the substrate 7 and is connected to a blower 12b.By operating the blower 12b, air at a temperature lower than the temperature of the outside air or the atmosphere inside the furnace is cooled. The pipe 12a is configured to blow against the lower surface of the board 7 (that is, the surface to which mounted components have already been soldered).

In this example furnace, the board 7 that has been transported to the main heating section A via the pre-heating section B has its upper surface -3 (i.e., the surface to which mounted components are to be soldered). is radiantly heated by a surface heater 5a, and its lower surface is heated by a pipe 1.
Forced cooling is performed by low temperature air blown from 2a. At this time, the cooling fan 11 also operates and continues to blow cold air along the conveyance direction outside the furnace outlet 1b, so that the airflow blown against the bottom surface of the substrate 7 is directed toward the furnace as shown by the arrow. The flow flows out to the exit ib side, and there is no adverse effect on the inside of the furnace.

Since the lower surface of the board 7 is forcedly cooled, the solder does not remelt, and therefore the problem of the already soldered mounted components falling is prevented.

FIG. 3 is a block diagram showing still another embodiment of the furnace.

In the case of this furnace, in the furnace shown in FIG. 2, hot air circulation means 13, 14 are provided independently in a part of the preheating section B and in the main heating section A, respectively.

In the hot air circulation means 13, a pipe 14a is inserted into the inlet Ia side of the furnace body from above to near the substrate 7, and is further connected to a blower 13c via an air heater 13b, and a blower is also installed at the boundary between the surface heaters 3a and 4a. A pipe 13d connected to 13c is inserted from above to near the board 7. When the blower 13c is operated, the airflow heated by the air heater 13b circulates in the direction of the arrow q in the figure, and the substrate 7
A convection current is formed that heats the top surface of the

In the hot air circulation means 14, a pipe 14a is inserted between the surface heaters 4a and 5a to near the substrate 7, and further connected to a blower 14c via an air heater 14b, and between the surface heater 5a and the outlet 1b of the furnace. Also, a pipe 14d connected to the blower 14c is inserted close to the substrate 7. When the blower 14c is operated, the airflow heated by the air heater 14 circulates in the direction of arrow r in the figure, and the substrate 7
A convection current is formed that heats the top surface of the

By disposing such hot air circulation means 13, 14, it is possible to effectively uniformize the temperature of the substrate 7 in the preheating section B, and in the main heating section A, the substrate 7 and the mounting mounted on it can be uniformly heated. Soldering is effective because it reduces the temperature difference between the components and increases the effect, and at the same time increases the effect of forced cooling on the lower surface of the board 7.

(Effects of the Invention) As is clear from the above explanation, the reflow oven of the present invention has
The configuration is such that a preheating section and a main heating section are formed by arranging a plurality of pairs of surface heaters vertically facing each other in the furnace length direction, and the object to be heated is formed between each pair of surface heaters. In the reflow oven in which the main heating section is transported, the heater on the lower side of the main heating section is removed or cooling is performed to introduce outside air or air at a temperature lower than the furnace atmosphere temperature into the lower part near the terminal end of the main heating section. By providing a means, when mounting components on both sides of the board, there is no need to re-melt the solder at the joints of components already mounted on one side.
As a result, the situation where the mounted components fall when removed from the main heating section A is reduced by 4 degrees.

Furthermore, since the temperature of the mounted components that have already been mounted is lowered, the effect of alleviating the thermal stress on the components can also be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the reflow oven of the present invention, Fig. 2 is a block diagram showing another embodiment, Fig. 3 is a block diagram showing still another embodiment, and Fig. 4 is a block diagram showing a conventional reflow oven. It is a block diagram of a reflow oven. 1...Furnace body, 2a, 2b, 3a, 3b
, 4a, 4b. 5a, 5b, 5b'... surface heater, 6...
Belt conveyor, 7... Substrate (heated object), 8...
Motor, 9... Drive roller, 10... Feeding roller, 11... Cooling fan, 12... Cooling means, 12
a...Pipe, 12b...Blower, 13.14...
-Hot air circulation means, 13a, 13d. 14a, 14b---Pipe, 13b, 14b...Air heater, 13c, 14c...Blower, A...Main heating section, B...Preheating section.

Claims (1)

[Claims] A preheating section and a main heating section are formed by arranging a plurality of pairs of surface heaters vertically facing each other in the furnace length direction, and the object to be heated is conveyed between each pair of surface heaters. In the reflow oven, the heater on the lower side of the main heating section is removed, or a cooling means is provided at the bottom near the terminal end of the main heating section for introducing outside air or air at a temperature lower than the temperature of the atmosphere in the furnace. A reflow oven characterized by: